1. Field of the Invention
The present invention relates to sheet conveying apparatuses, and more particularly to a sheet conveying apparatus capable of conveying a rectangular sheet in such a manner that a center line of the sheet relative to a conveyance direction of the sheet coincides with a predetermined center line for conveyance.
2. Description of the Related Art
In Japanese Patent Application No. 6-101236, the present applicant proposed an invention relating to a sheet discharging apparatus for a printing machine. This invention has been made public in Japanese Patent Publication No. 7-309496. This invention will be explained referring to FIGS. 3 to 8.
As illustrated in FIG. 3, an outlet 300a of a printing machine 300 is connected to an inlet of a sheet discharging apparatus 101 through a sheet conveying apparatus 100. The sheet conveying apparatus 100 has plural endless belts driven by a conveying motor. A post card as a sheet is printed by the printing machine 300, and conveyed by the sheet conveying apparatus 100, and then received in the sheet discharging apparatus 101. Ink on the post card as received is dried while the card is supported and conveyed in the sheet discharging apparatus 101. Then, the post card is dropped onto a tray 116 situated in a lower part of the sheet discharging apparatus 101, and stored therein.
As illustrated in FIG. 5, the sheet conveying apparatus 100 includes a conveying surface 102 for conveying a sheet. In the center of the conveying surface 102, an opening 103 is formed along a conveying direction. That is, two sheet guiding plates are situated along a direction perpendicular to the conveying direction at a predetermined distance away from each other, thereby forming the conveying surface 102. The distance between the two sheet guiding plates can be optionally adjusted. In the opening 103, sheet conveying means is situated. The sheet conveying means 103 includes a pair of pulleys 104 and three belts connecting the pulleys. The belts are parallel to each other. Upper surfaces of the belts contacting a bottom surface of the sheet 106 coincides with the conveying surface 102. The belts 105 convey the sheet 106 with the upper surfaces thereof contacting the bottom surface of the sheet 106.
As illustrated in FIG. 4, the sheet discharging apparatus 101 has, as a main body, a frame 110 approximately in a form of a box. On an upper portion of the frame 110, two shafts 111 are situated along two side edges of the sheet to be conveyed, respectively. Each shaft 111 has supporting means 112 comprising four plates.
In the frame 110, a pair of upper and lower driving axes 113 is situated below each of the shafts 111. The driving axes 113, 113 of the same pair are connected by two belts 114. Each of the belts 114 has many receiving flaps 115 formed at a predetermined distance therebetween. As illustrated in FIG. 6, in a view perpendicular to the conveying direction, a distance between the right and the left belts 114, 114 is relatively wide in an upper portion and approximately coincides with a width of the sheet 106 in a lower portion.
A discharging tray 116 is drawably situated at the bottom of the frame 110.
The sheet 106, after being printed thereon by a not-shown printing machine, is discharged to the outside of the machine. The printed sheet 106 discharged from the printing machine is placed on the conveying surface 102 of the sheet conveying apparatus 100. The belt 105 moves while contacting the bottom surface of the sheet 106, thereby moving the sheet 106 along the conveying surface 102. The sheet is positioned while being guided by the sheet guiding plates at both side edges thereof, and conveyed to the sheet discharging apparatus 101. The sheet 106 is supported by the pair of the supporting means 112 of the sheet discharging apparatus 101. Upon rotation of the shaft 111, the sheet is downwardly conveyed and held by the receiving flaps 115 therebetween. Moving belts 114 convey the sheet downwardly. Ink printed on the sheet is dried during conveyance, and then the sheet is dropped onto the discharging tray 116 to be stacked therein.
As illustrated in FIG. 5, a center line L1 of the rectangular sheet 106 as discharged from the printing machine is parallel to the conveying direction, but this does not necessary coincide with a center line L2 of the sheet conveying apparatus 100 for conveyance. Conventionally, if the distance between the sheet guiding plates of the sheet conveying apparatus 100 is arranged to coincide with the width of the sheet 106, the center line L1 of the sheet 106 in the conveyance direction is to coincide with the center line L2 for conveyance while the sheet 106 is conveyed to pass through the distance. However, as a matter of fact, it is difficult to make the center line L1 in the conveyance direction of the sheet 106 to coincide with the center line L2 precisely by using the sheet guiding plates.
Namely, the distance between the sheet guiding plates is adjustable according to the width of the sheet 106; therefore, it is inevitable that irregularity may occur in positioning the sheet guiding plates due to such adjustability. Hence, in the case where a sheet of a size is conveyed, it is difficult to always place the sheet guiding plates in constant positions determined according to the size. Further, the distance between the sheet guiding plates must be adjusted fairly broader than the width of the sheet to allow the sheet to pass through the distance. Thus, in the conventional sheet conveying apparatus, the distance between the sheet guiding plates is adjusted broader than the width of the sheet to be guided, and the distance actually adjusted may include irregularity.
Accordingly, in the case where the center line of the rectangular sheet does not coincide with that of the sheet conveying apparatus when the sheet is discharged from the printing machine, it is difficult to correct the position of the sheet by the sheet guiding plates so that the center line of the sheet coincides with that of the sheet conveying apparatus.
Suppose that, as illustrated in FIG. 6, the sheet 106 is fed into the sheet discharging apparatus 101 in such a manner that the center line L1 does not coincide with the center line L2. As illustrated in FIG. 7, two side edges of the sheet 106 are not positioned equally to the pair of the supporting means 112, respectively. That is, in FIG. 7, the right side edge of the sheet 106 insufficiently engages the right supporting means, but the left side edge of the sheet 106 sufficiently engages the left supporting means. Therefore, when the supporting means 112 rotate in the direction shown by arrows in the drawing, as illustrated in FIG. 8, the right side edge of the sheet 106 leaves the supporting means 112, thereby falling onto the receiving flap 115. Then, the left side edge of the sheet 106 engages the left supporting means 112. Accordingly, the sheet 106 inclines relative to the pair of the belts 114, 114, so that the sheet can not be appropriately passed from the supporting means to the belts.
An object of the present invention is to provide a sheet conveying apparatus capable of conveying the rectangular sheet in such a manner that the center line of the sheet coincides with a center line thereof for conveyance.